Charged Microparticles Research Articles

Observation of dust acoustic shock wave in a strongly coupled dusty plasma

Dust acoustic shock wave is observed in a strongly coupled laboratory dusty plasma. A supersonic flow of charged microparticles is allowed to perturb a stationary dust fluid to excite dust acoustic shock wave. The evolution process beginning with steepening of initial wave front and then formation of a stable shock structure is similar to the numerical results of the Korteweg-de Vries-Burgers equation. The measured Mach number of the observed shock wave agrees with the theoretical results. Reduction of shock amplitude at large distances is also observed due to the dust neutral collision and viscosity effects. The dispersion relation and the spatial damping of a linear dust acoustic wave are also measured and compared with the relevant theory.

Trapping and Driving Individual Charged Micro-particles in Fluid with an Electrostatic Device.

A variety of micro-tweezers techniques, such as optical tweezers, magnetic tweezers, and dielectrophoresis technique, have been applied intensively in precise characterization of micro/nanoparticles and bio-molecules. They have contributed remarkably in better understanding of working mechanisms of individual sub-cell organelles, proteins, and DNA. In this paper, we present a controllable electrostatic device embedded in a microchannel, which is capable of driving, trapping, and releasing charged micro-particles suspended in microfluid, demonstrating the basic concepts of electrostatic tweezers. Such a device is scalable to smaller size and offers an alternative to currently used micro-tweezers for application in sorting, selecting, manipulating, and analyzing individual micro/nanoparticles. Furthermore, the system offers the potential in being combined with dielectrophoresis and other techniques to create hybrid micro-manipulation systems.Electronic supplementary materialThe online version of this article (doi:10.1007/s40820-016-0087-3) contains supplementary material, which is available to authorized users.

Complex Plasma Research under Microgravity Conditions: PK‐3 Plus Laboratory on the International Space Station

AbstractComplex (dusty) plasmas are composed of weakly ionised gas and charged microparticles and represent the plasma state of soft matter. Due to the “heavy” component – the microparticles – and the low density of the surrounding medium, the rarefied gas and plasma, it is necessary to perform experiments under microgravity conditions to cover a broad range of experimental parameters which are not available on ground. The investigations have been performed onboard the International Space Station (ISS) with the help of the “Plasma Crystal‐3 Plus” (PK‐3 Plus) laboratory. It was perfectly suited for the formation of large stable liquid and crystalline systems and provided interesting insights into processes like crystallisation and melting, laning in binary mixtures, electrorheological effects due to ac electric fields and projectile interaction with a strongly coupled complex plasma cloud. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Уединенная волна в структуре заряженных микрочастиц

Уединенная волна в структуре заряженных микрочастиц

単極イオン溶液における荷電微粒子の運動解析

単極イオン溶液における荷電微粒子の運動解析

Confinement of charged microparticles in a gas flow by the linear Paul trap

In this paper, we present the experimental results demonstrating the charged microparticles confinement in an electrodynamic trap in a gas flow and prove the selective possibility of these traps to capture charged microparticles in gas flows in a wide range of microparticle and trap parameters.

Microparticle charging in dry air plasma created by an external ionization source

In the present paper the dust particle charging is studied in a dry air plasma created by an external ionization source. The ionization rate is changed in the range 101-1020 cm-3s-1. It is found that the main positive ion of the plasma is O+4 and the main negative ones are O−2 and O−4. The point sink model based on the diffusion-drift approach shows that the screening potential distribution around a dust particle is a superposition of four Debye-like exponentials with four different spatial scales. The first scale almost coincides with the Debye radius. The second one is the distance, passed by positive and negative plasma components due to ambipolar diffusion in their recombination time. The third one is defined by the negative ion conversion and diffusion. The fourth scale is described by the electron attachment, recombination and diffusion at low gas ionization rates and by the recombination and diffusion of negative diatomic ions at high ionization rates. It is also shown that the electron flux defines the microparticle charge at high ionization rates, whereas the electron number density is much less than the ion one.

Effective forces and pseudopotential wells and barriers in the linear Paul trap

The paper presents the numerical studies of effective forces acting on a charged microparticle inside the linear Paul trap in gas media. The locations of the microparticle trapping as the dependence on microparticle and trap parameters have been studied.

Physics Essay: The Nature of Charge, Principle of Charge Interaction and Coulomb's Law

<p class="1Body">What is “electronic charge”? Why there are two kinds of charges? Why do the same charges repel, and dissimilar charges attract each other? Why does their behavior agree with Coulomb's Law? These are among the most basic questions of physics. Let us assume the existence of a kind of microparticle in the universe, which we can call an electon for our purposes here. Three situations are possible: if an object contains a surplus of electons, it will be positively charged; if a deficit of electons, it will be negatively charged; if an object contains electons equal to its expected value, in the saturated state, it is neutral. The charged objects, containing these electons, have the ability to exchange charged or uncharged microparticles in order to achieve a neutral state. The acting force between two charged objects comes from the exchange of charged and uncharged microparticles. The same charges repel, and dissimilar charges attract each other. The value of force is consistent with Coulomb's Law. The material homogeneous between two charged objects affects the value of the acting force between them, but does not affect the direction.</p>

Predicting electrostatic charge on single microparticles

Electrostatic charge significantly affects the adhesion of microparticles. Presently the nature of surface charge distribution on a single microparticle and the effect of electrostatic charge as a contributor to its adhesion are not well understood. As a result of the strong discrepancies between the experimental adhesion measurements data and theoretical predictions over the years, some questions regarding adhesion force contributors in charged microparticles still remain unresolved. One reason for the current state of knowledge is difficulties associated with accurate measurement of particle charge. In current work, a non-contact and non-destructive opto-ultrasonic method is presented and employed to predict the equivalent bulk charge on a single charged micro-scale toner particle and to provide insight into the nature of charge distribution on its surface. From the vibrational spectral response of the particle to the ultrasonic excitation of the substrate, irregular shifting patterns of the vibrational (in-plane rocking) resonance frequencies of the particle are observed for the applied levels of substrate surface voltage (0–1500V), implying non-uniform (patch-charges) surface charge distribution on the microparticle. For predicting the equivalent bulk charge on a single patch-charged toner particle from this resonance frequency shift, a mathematical model is developed and employed. In conclusion, it is demonstrated that, in a non-invasive/non-contact manner, the total charge on a single microparticle can be predicted using the presented experimental approach, and evidence for the non-uniform charge distribution on a single particle is observed and reported.

Mechanism of immunoglobulin G adsorption on polystyrene microspheres

The adsorption of polyclonal immunoglobulin G (IgG) on negatively charged polystyrene microparticle suspension (latex) was studied by using the Laser Doppler Velocimetry (LDV) measurements. Using this technique, the dependence of the electrophoretic mobility of particles on the IgG concentration in the suspension was measured for various ionic strengths and pH 3.5. The increase in the electrophoretic mobility was quantitatively interpreted in terms of the 3D electrokinetic model. On the other hand, the maximum coverage of IgG on latex was determined using the depletion method based on AFM imaging. It was shown that IgG adsorption was irreversible and that its maximum coverage on the microspheres increased from 1.4mgm−2 for 0.001M NaCl to 2.0mgm−2 for 0.15M NaCl. This was interpreted in terms of reduced electrostatic repulsion among adsorbed molecules. The stability of IgG monolayers on the particles was confirmed in separate experiments where changes in its electrophoretic mobility were monitored over prolonged time periods. Additionally, the acid-base properties of the IgG monolayers on latex were determined in pH cycling experiments. The isoelectric point of the IgG monolayers on the microspheres was 4.8. The results obtained in this work indicate that basic physicochemical characteristics of IgG can be acquired via electrophoretic mobility measurements using microgram quantities of the protein.

Investigation of the stabilizer elimination during the washing step of charged PLGA microparticles utilizing a novel HPLC-UV-ELSD method

Quantification of stabilizer content in microparticles and other products is of great importance for formulation development, drug product quality control as well as for reproducible manufacturing. A fast and sensitive HPLC method with evaporative light scattering detection (ELSD) capable of detecting docusate sodium (DOSS), poly (lactic-co-glycolic acid) (PLGA; Resomer RG 503 H) and R-1,2-dioleoyloxy-3-trimethylammonium-propane (DOTAP) in a single run was successfully developed. In contrast to previously described methods, hydrolysis of PLGA as pretreatment is not necessary, thereby enabling accurate quantification of stabilizer next to the intact matrix polymer.This method was used to investigate the impact of washing procedures of polymeric microparticles manufactured either with anionic stabilizer DOSS or with cationic stabilizer DOTAP. High amounts of DOSS were detected in the washing water. This finding was consistent with the result that no DOSS could be detected in the washed and dried microparticles (<limit of detection).In contrast, DOTAP was hardly measurable in the washing water during all washing cycles. However, DOTAP could be quantified in dried particles. The ratio of DOTAP to dry particle mass was approximately 1:10.This is most probably due to the different polymer surfactant interactions (e.g. charge) and the different hydrophilicity of the stabilizers used.

Drag force on micron-sized objects with different surface morphologies in a flow with a small Reynolds number

Drag force on micron-sized particles in an aqueous medium was determined and compared with that predicted by the Stokes’ law. Effect of a number of parameters such as surface morphology of particles, particle size, and so on on the drag force acting on the microparticles in an aqueous medium was systematically investigated. Surface morphology was found to strongly affect the drag force working on the microparticles. In addition surface charge, roughness, and physical nature of microparticles were also found involved in the alteration of the drag force.

AC Electric Field-Induced Trapping of Microparticles in Pinched Microconfinements.

The trapping of charged microparticles under confinement in a converging-diverging microchannel, under a symmetric AC field of tunable frequency, is studied. We show that at low frequencies, the trapping characteristics stem from the competing effects of positive dielectrophoresis and the linear electrokinetic phenomena of electroosmosis and electrophoresis. It is found, somewhat unexpectedly, that electroosmosis and electrophoresis significantly affect the concentration profile of the trapped analyte, even for a symmetric AC field. However, at intermediate frequencies, the microparticle trapping mechanism is predominantly a consequence of positive dielectrophoresis. We substantiate our experimental results for the microparticle concentration distribution, along the converging-diverging microchannel, with a detailed theoretical analysis that takes into account all of the relevant frequency-dependent electrokinetic phenomena. This study should be useful in understanding the response of biological components such as cells to applied AC fields. Moreover, it will have potential applications in the design of efficient point-of-care diagnostic devices for detecting biomarkers and also possibly in some recent strategies in cancer therapy using AC fields.

Microparticle injection effects on microwave transmission through an overly dense plasma layer

Microparticles injected into a plasma have been shown to deplete the free electron population as electrons are collected through the process of microparticles charging to the plasma floating potential. However, these charged microparticles can also act to scatter electromagnetic signals. These experiments investigate microwave penetration through a previously impenetrable overly dense plasma layer as microparticles are injected and the physical phenomena associated with the competing processes that occur due to electron depletion and microwave scattering. The timescales for when each of these competing processes dominates is analyzed in detail. It was found that while both processes play a significant and dominant role at different times, ultimately, transmission through this impenetrable plasma layer can be significantly increased with microparticle injection.

Confinement of the charged microparticles by alternating electric fields in a gas flow

This paper presents the simulation and experimental results of charged microparticles dynamics in electrodynamic traps in a gas flow at atmospheric pressure. For the first time the capture and confinement of charged microparticles in a linear Paul trap has been experimentally confirmed at atmospheric pressure in gas flows. The regions of the microparticle, linear Paul trap and gas flow parameters needed for microparticle confinement have been obtained and experimentally tested.

Patterning Microparticles on a Template of Aggregated Cationic Dye

Patternwise aggregation of charged molecules on a surface is potentially a facile approach to generate a template on which to pattern oppositely charged microparticles. We report on the patterning of silica microparticles by a system comprising a photopatternable copolymer and an aggregate forming penta-cationic cyanine dye. A thin film of the copolymer, composed of a molar excess of styrenesulfonic acid oxime ester to cross-linkable glycidyl methacrylate monomomers, was exposed through a mask and neutralized, resulting in a pattern of hydrophobic areas, and where exposed, a hydrophilic cross-linked film with sodium poly(styrenesulfonate) domains. The occurrence and locus of aggregation of an aqueous solution of the dye, applied to the patterned surface was established by absorbance and fluorescence spectroscopy and atomic force microscopy. In exposed areas, dye is imbibed and aggregation induced in sodium styrenesulfonate domains internal to the layer, whereas in the unexposed areas the dye aggregates on the hydrophobic surface. Aqueous anionic silica microparticles applied to the dye treated patterned surface and then rinsed, are retained in the unexposed areas having cationic surface aggregates, but rejected from the exposed areas with internal dye aggregates as these areas retain net negative charge. Mask exposure, absent dye treatment, did not result in patterning as negatively charged microparticles were nowhere retained, and positively charged particles were everywhere retained. The extent of surface coverage by the dye in unexposed areas was deposition time dependent, and ranged from isolated patches covering about 20 percent of the polymer surface to a surface saturated layer, with silica particle patterning robust over the range of dye surface coverages studied. The force requirements to pattern the denser than water silica microparticles are identified, and particle and polymer film surface potentials that meet the critical repulsion force requirement are mapped using an established sphere-to-flat surface electric double layer (EDL) model.

Osteogenic evaluation of collagen membrane containing drug-loaded polymeric microparticles in a rat calvarial defect model.

The aim of this study was to develop a functional collagen membrane that is treated with poly (lactic-co-glycolic acid) (PLGA) nanoparticles loaded with dexamethasone (DEX) as a bioactive molecule for guided bone regeneration (GBR). The DEX-loaded PLGA microparticles prepared using water-in-oil standard emulsion method were precoated with positively charged polyethylenimine molecules and later immobilized onto the surface of the collagen membrane; the microparticles were physically immobilized using counter charges of positively charged PLGA microparticles and the negatively charged collagen membrane surface. The release profile of DEX over a 4-week immersion study indicated an initial burst release followed by a sustained release. The performance of this system was investigated using rats with calvarial bone defects. The in vivo evaluation of the defects filled with membrane containing DEX-loaded PLGA microparticles indicated enhanced volume and quality of new bone formation compared with defects that were either unfilled or filled with membrane alone. This innovative platform for bioactive molecule delivery more potently induced osteogenesis, which may be exploited in implantable membranes for stem cell therapy or improved in vivo performance. In conclusion, this newly developed collagen membrane treated with drug-loaded PLGA microparticles might be applicable as a promising bone graft substitute for GBR.

Charge contribution to patch-charged microparticle adhesion

Microparticle adhesion influenced by electrostatic charge has been a significant research interest for over past three decades or so in a wide spectrum of areas of interest from manufacturing (electrophotography, powder technology, metallurgy, and semi-conductor manufacturing) to natural phenomena (desert sandstorms and northern lights (auroras)). However, over the years, as a result of the strong discrepancies between the experimental adhesion measurements data and theoretical predictions, some key issues regarding the contributors of adhesion forces in charged microparticles and the nature of surface charge distribution still remain unresolved. In the current work, a non-contact ultrasonic approach is presented and employed for understanding the nature of charge distribution on a single microparticle and determining the effect of electrostatic charge on its adhesion in a non-invasive manner. From the vibrational spectra of the charged particle response to the ultrasonic substrate oscillations under various electrostatic loading conditions, three distinct shifting patterns of vibrational (rocking) resonance frequencies are observed for each level of applied substrate surface voltage, implying an un-symmetric force field on the particle, thus depicting non-uniform non-symmetric surface charge distribution on its surface. Also, a simple mathematical model was presented and employed for predicting the equivalent bulk charge on a single microparticle (toner) from resonance frequency shifts. In summary, it is found that the charge levels reported here are consistent with the previously published data, and it is demonstrated that, in a non-invasive manner, non-uniform charge distribution on a single microparticle can be observed and its total charge can be predicted.

Immobilization of endo-inulinase on poly-d-lysine coated CaCO3 micro-particles

Inulinase is widely applied to produce high fructose syrup (HFS) which is used in the food and pharmaceutical industries. Numbers of different techniques such as physical adsorption, entrapment, ion exchange and covalent bonding have been used to immobilize enzymes on solid supports. In this study, an efficient technique for inulinase immobilization was developed which consists of adsorbing a cationic polyelectrolyte poly-d-lysine (PDL) on negatively charged calcium carbonate micro-particles (CaCO3-MPLs) and immobilizing inulinase through electrostatic interactions between negatively charged amino acids of inulinase and positively charged [CaCO3/PDL-MPLs] complex. The most effective CaCO3-MPLs which had the smallest diameter were manufactured using ultrasonic spray pyrolysis; a new application of this method to manufacture the enzyme support. This method enabled us to reduce the particle size to 2.9μm which showed the highest average protein loading capacity of 21.3±0.1mg or 32.0±1.3U enzyme per gram of CaCO3-MPLs. Two sets of binding sites are available on the [CaCO3/PDL-MPLs] for inulinase, both resulted in positive cooperation with Hill coefficients of 2.3 and 6.8 for the first and second sets of binding sites, respectively. For the immobilized enzyme, the optimum temperature of activity increased from 50 to 55°C and immobilization resulted in higher thermal stability. Storage stability of immobilized inulinase increased more than two-fold as demonstrated by half-lives (t1/2) which increased from 65.2 to 148days for the free and immobilized inulinases, respectively.